1. Field of the Invention
The present disclosure relates to adhesives, and particularly to pressure sensitive adhesives derived from energy-curable polymer-forming compositions.
2. Background of the Related Art
Pressure sensitive adhesives are known in the art. A pressure sensitive adhesive (“PSA”) is one which in dry form is aggressively and permanently tacky at room temperature and which firmly adheres to a variety of dissimilar surfaces upon mere contact without the need of more than finger or hand pressure. PSA requires no activation by heat or solvents. It should have a sufficiently cohesive holding and elastic nature so that it can be removed from a surface without leaving a residue. PSAs are generally used in adhesive tapes and labels. An adhesive tape typically includes a substrate, i.e., a backing, to which the PSA is applied. Usually a primer is used to treat the surface of the backing to provide greater anchoring of the PSA. If the tape is stored in a rolled configuration the opposite surface of the backing is generally coated with a release coating, such as silicone, to allow unrolling of the tape.
Various types of PSAs are known. For example, PSA can be made from tackified natural or synthetic rubbers, ethylene-vinyl acetate copolymers, acrylics, vinyl acetate copolymers, silicones, and polymerized vinyl alkyl ethers.
Hot melt type PSAs are typically heated to a temperature sufficient to render the PSA sufficiently fluid so that it can be applied to a substrate.
Solution type PSA's are generally dissolved in a solvent to form a fluid which can be applied to a substrate. The solvent is thereafter evaporated to form the PSA coating.
Energy-curable formulations for making PSAs typically include unsaturated monomers or oligomers, especially acrylate type compounds. Such formulations also typically include a photoinitiator which is responsive to, for example, ultraviolet radiation (UV) for initiating polymerization. Such formulations are applied to a substrate as a fluid prepolymer, and are thereafter polymerized to form the PSA layer.
The properties of the PSA can be tailored by altering the type and/or composition percentage of the components in the formulation. However, it is not uncommon that improvement in one property of the PSA results in a detrimental change in another. For example, to increase the peel strength of the PSA a higher softening point tackifier can be used, or the content of di- or multi-functional oligomer resin can be increased. However, in each case, the PSA tack is reduced. What is needed is a method which can be used to improve the peel strength, while not incurring a corresponding detriment to the tack.